There have been continuing attempts to improve techniques for removing fine particulates from biomass fuel oxidation-exhaust gas streams. The conventional method in biomass combustion has been to use boilers in conjunction with dry electrostatic precipitators to collect fly ash. The fly ash has often been comprised of partially combusted organic matter mixed in with the inorganic constituents. These semi-organic particles have traditionally precipitated on collecting surfaces in dry precipitators forming potential fire and maintenance hazards. Among the recent improvements is the utilization of condensing wet electrostatic precipitators wherein the particulates carried by an incoming gas stream are entrained in condensate formed on walls of the precipitator and are flushed from the walls for collection. Also known is a down-flow type of WESP in which the water droplets move concurrently with the gas and provide a cleaning action when deposited together with particles.
Despite such improvements, however, there remains a need for an improved apparatus and methods for eliminating all or substantially all of a particulate matter from a gas stream. Furthermore, a need exists for removing particulate matter and environmentally hazardous gases produced from the combustion of biomass and biomass supplemented fuel sources. This invention seeks to provide such an apparatus.
Conventional systems utilize three separate and distinct pieces of equipment in order to treat effluent gases from the oxidation of biomass derived fuels. These three pieces of equipment are an electrostatic precipitator, an acid gas scrubber, and a selective catalytic reduction reactor. In the conventional system, the electrostatic precipitator is used to remove, via electrostatic collection, biomass particulate matter resulting from the combustion of biomass. An acid gas scrubber located either upstream or downstream of the electrostatic precipitator is used to chemically introduce to the gasses strong reducing agents capable of chemically neutralizing the acid gas emissions that originate from the combustion of biomass. A selective catalytic reduction reactor is then required to treat the nitrogen oxide emissions originating from the combustion of biomass. This treatment of the nitrogen oxide emissions is done through the introduction of a strong reducing agent such as ammonia into the gas stream.
These three separate pieces of equipment have various physical interconnections and multiple control connections that increase the cost and complexity of installation and operation. For this reason, a single apparatus that could perform the functions the three conventional pieces of equipment would be an important improvement in the art.